Issue when creating PhysicsConstraint between a SkeletalMeshActor and StaticMeshActor

Development World Creation
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1

Hi there,

I am trying to dynamically attach an object to a skeletal component (a hand).

For this I am using Physics Constraints since physics will be important for me. However, when I attach the object to the hand it snaps to an offseted position (see video). In the video the Skeletal Mesh was part of a Character.

I also tested this where the skeletal mesh was an individual Actor (a floating fixed hand in the air) and the same issue appeared (see video).

However, if I use a StaticMesh to attach the object (a floating fixed brown cylinder), it works as supposed to: the constraint is created, and the object remains in its current position (see video).

The code for creating the constraint:

	// .H
	// Constraint component
	UPhysicsConstraintComponent* MConstraintComp;
	// Hand skeleton as fixed actor
	ASkeletalMeshActor* HandSkelAct;
	// Brown cylinder as fixed static mesh actor
	AStaticMeshActor* StaticMeshAct1;
	// Gray cylinder falling down and attaching the constraint to
	AStaticMeshActor* StaticMeshAct2;

	// .CPP
	// CONSTRUCTOR
	// Create the physics constraint
	MConstraintComp = CreateDefaultSubobject<UPhysicsConstraintComponent>(TEXT("MFixatingGraspConstr"));
[..]

// Constraint action binding function
void MyCharacter::OnCreateConstraint()
{
	if (!bAttached)
	{
		//Set World Location
		MConstraintComp->SetWorldLocation(HandSkelAct->GetActorLocation());

		//Attach
		MConstraintComp->AttachToComponent(HandSkelAct->GetRootComponent(), FAttachmentTransformRules::KeepWorldTransform);

    	// Add the constraint components
		MConstraintComp->SetConstrainedComponents(
			HandSkelAct->GetSkeletalMeshComponent(), NAME_None, /* OR StaticMeshAct1->GetStaticMeshComponent(), NAME_None,*/
			StaticMeshAct2->GetStaticMeshComponent(), NAME_None);

		bAttached = true;
		PrintGreen(TEXT("Attached!"));
	}
	else if (bAttached)
	{
		MConstraintComp->BreakConstraint();
		bAttached = false;
		PrintRed(TEXT("Detached!"));
	}
}

Am I doing something wrong, or this is a bug?

Thanks!

2

Hey ionbordura,

It looks like the two physics objects (the hand and the Skeletal Mesh) are reacting to each other.

I’d recommend trying a couple things. The first is to create a collision channel for either the hands or the pickup Actors so the other wont react to it.

You can also try turning off the collision of the pickup Actor when it is being attached and see if that prevents the result of the first video from happening.